Electric Heating Sequence Of Operations - York J ZJ Series Instruction Manual

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Instruction manual (76 pages)

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(Anti-short cycle delay), and stop the condenser fans. If the call

for cooling is still present at the conclusion of the ASCD, the

UCB will re-energize the halted compressor.

Should a high-pressure switch open three times within two

hours of operation, the UCB will lock-out the compressor.

Low-Pressure Limit Switch

The low-pressure limit switch is not monitored during the initial

30 seconds of a cooling system's operation. For the following

30 seconds, the UCB will monitor the low-pressure switch to

ensure it closes. If the low-pressure switch fails to close after

the 30-second monitoring phase, the UCB will de-energize the

compressor, initiate the ASCD, and stop the condenser fans.

Once the low-pressure switch has been proven (closed during

the 30-second monitor period described above), the UCB will

monitor the low-pressure limit switch for any openings. If the

low-pressure switch opens for greater than 5 seconds, the UCB

will de-energize the compressor, initiate the ASCD, and stop

the condenser fans.

If the call for cooling is still present at the conclusion of the

ASCD, the UCB will re-energize the halted compressor.

Should a low-pressure switch open three times within one hour

of operation, the UCB will lock-out the =compressor.

Evaporator Low Limit

During cooling operation, if the Evaporator Low Limit Sensor

(EC1) (Located on the Suction Line at the Evaporator Coil.)

detects a temperature below 26 Deg. F (default), the UCB will

de-energize the compressor, initiate the ASCD, and stop the

condenser fans. If the call for cooling is still present at the

conclusion of the ASCD, the UCB will re-energize the halted

compressor. Should the UCB detect the evaporator low limit

sensor (EC1) falling below 26 Deg. F (default) three times

within two hours of operation, the UCB will lock-out the

compressor.

Low Ambient Cooling

To determine when to operate in low ambient mode, the UCB

has an Outdoor Air Temperature Sensor (OAT) with a low

ambient setpoint at 45ºF (default). When the OAT Sensor

senses a temperature below the low ambient setpoint and the

thermostat is calling for cooling, the UCB will operate in the low

ambient mode.

Low ambient mode operates the compressors in this manner:

10 minutes on, 5 minutes off. The indoor blower is operated

throughout the cycle. The 5-minute off period is necessary to

defrost the indoor coil.

Low ambient mode always begins with compressor operation.

Compressor minimum run time may extend the minutes of

compressor operation. The off cycle will begin immediately

following the elapse of the minimum run time.

When operating in low ambient mode, an evaporator low limit

sensor (EC1) temperature below 26ºF will de-energize the

Johnson Controls Ducted Systems

compressor. If the call for cooling is still present at the end of

the ASCD and the and the evaporator temperature sensor

(EC1) temperature is above 26°F, the unit will resume

operation.

Safety Controls

The unit control board monitors the following inputs for each

cooling system:

An evaporator low limit sensor (EC1) (Located on the

Suction Line at the Evaporator Coil.) to protect against low

evaporator temperatures due to a low airflow or a low

return air temperature, set at 26°F.

A high-pressure switch to protect against excessive

discharge pressures due to a blocked condenser coil or a

condenser motor failure, (opens at 625 ± 25 psig).

A low-pressure switch to protect against loss of refrigerant

charge, (opens at 50 ± 5 psig).

The above pressure switches are hard-soldered to the unit. The

refrigeration systems are independently monitored and

controlled. On any fault, only the associated system will be

affected by any safety/preventive action. The other refrigerant

system will continue in operation unless it is affected by the

fault as well.

The unit control board monitors the temperature limit switch of

electric heat units and the temperature limit switch and the gas

valve of gas furnace units.

Compressor Protection

In addition to the external pressure switches, the compressors

also have inherent (internal) protection. If there is an abnormal

temperature rise in a compressor, the protector will open to shut

down the compressor. The UCB incorporates features to

minimize compressor wear and damage. An Anti-Short Cycle

Delay (ASCD) is utilized to prevent operation of a compressor

too soon after its previous run. Additionally, a minimum run time

is imposed any time a compressor is energized.

The ASCD is initiated on unit start-up and on any compressor

reset or lock-out.

Reset

Remove the call for cooling, by raising thermostat setting higher

than the conditioned space temperature.